Background -Calcinosis cutis is well recognized in dogs with endogenous hyperglucocorticism and iatrogenic hyperglucocorticism, but the pathogenesis is still unclear.Objectives -The objectives of the study were to identify possible correlations between histopathological patterns of dermal mineralization in skin biopsies and underlying causes for calcinosis cutis in dogs, as well as to determine breed predilection and age of onset for dogs within a hospital population. In addition, mineral analysis was performed on four biopsy samples.Animals -Forty-six dogs with histopathologically confirmed calcinosis cutis were evaluated.Methods -Medical records and histological sections of dogs with calcinosis cutis diagnosed by histopathology over a 21 year period were reviewed. Infrared spectrometry was used to identify the mineral in the paraffin blocks. Exact chi-squared test was used to identify breed predispositions, while a Mann-Whitney U-test was used to identify age correlations.Results -Labrador retrievers, Rottweilers, boxers and Staffordshire terriers were the breeds most commonly affected in this study. Most dogs had either an exogenous or an endogenous source of corticosteroids, with the exception of five dogs with renal insufficiency. In the majority of cases, mineralization was found throughout the entire dermis. The average age of onset of calcinosis cutis for dogs with endogenous hyperglucocorticism was older than that of dogs with iatrogenic hyperglucocorticism. Using infrared spectrometry, apatite crystals were found to be the source of mineral.Conclusions and clinical importance -There was no observable difference in the histopathological pattern of calcinosis cutis from dogs with endogenous hyperglucocorticism versus iatrogenic hyperglucocorticism. While glucocorticoid therapy appears to predispose dogs to developing calcinosis cutis, it remains unclear whether there is a specific dose or combination of factors that initiates the mineral deposition. Furthermore, the mineral deposition in dogs with calcinosis cutis was found to be apatite.